Issue 58

Q.-C. Li et alii, Frattura ed Integrità Strutturale, 58 (2021) 1-20; DOI: 10.3221/IGF-ESIS.58.01

experimentally during hydraulic fracturing operations. Li et al. [11] numerically investigated factors affecting fracture propagation during the multi-cluster staged fracturing for shale reservoir using cohesive elements with ABAQUS FEM software. The investigation reveals that the cluster spacing between the adjacent hydraulic-induced fractures is the most important factor. Chang et al. [12] carried out a series of laboratory experiments to investigate the effectiveness of oriented perforation fracturing, and it showed that the fractures formed by oriented perforation fracturing technology tend to stimulate more reservoir volume. Zhu et al. [13] studied the factors affecting initiation pressure of unconventional reservoirs with a finite element model of hydraulic-induced fracture for the cased wells with the oriented perforations. Li et al. [14] analyzed the reorientation mechanism of hydraulically induced fracture with the coupling finite element model, and the investigation results showed that difference between the maximum and the minimum horizontal principal stresses affects the fracture morphology large. Although these investigations are particularly useful and helpful, there is a lack of detailed research on factors affecting reorientation of fractures during hydraulic fracturing operations with oriented perforation in shale reservoirs. In other words, investigation on the fracture reorientation during reservoir stimulation through hydraulic fracturing is not deep enough. Therefore, it is important and necessary to conduct relevant research.

Figure 1: Schematic of fracture reorientation during hydraulic fracturing operation with oriented perforations. A: fracture initiation; B: fracture propagation; C: fracture reorientation; D: proppant retention within fracture.

In addition, the interaction between fractures during fracturing operation is also an important factor affecting the final fracture morphology in reservoir. Therefore, in-depth analysis of the interaction between fractures is valuable for understanding the formation mechanism of complex fracture network during the fracturing operation. Up till now, some progress has been made by so many scholars in this area. However, current investigations focus on the interaction between natural fractures and hydraulic fractures during fracturing operation, rather than interaction between hydraulically induced fractures. Zhou et al. [15] analyzed crack coalescence in rocks with defects by uniaxial compression experiments and found that crack coalescence can occur in nearly all samples, but the mechanism is different for different types of rocks. Yu et al. [16] numerically analyzed the interaction between fractures during fracturing in tight sandstone reservoir. It was found that obvious interaction occurs between hydraulically induced fractures, and the reservoir pressure is the dominant factor affecting the interaction between fractures. Zhang et al. [17] analyzed factors affecting propagation of natural fracture by XFEM method, it is found that natural fracture propagates easily with the decrease of dip angle and stress difference. Arash [18] investigated the effect of natural fracture on propagation of hydraulically induced fractures, and the investigation results show that interaction between natural fracture and hydraulically induced fracture is the key condition resulting in complex fracture network. Nevertheless, considering that interaction between hydraulic fractures is not the focus of the present work, so related investigation is not carried out herein. In the present work, the coupled finite element model (FEM) used for investigating reorientation of the hydraulically induced fracture in shale reservoirs was developed by using the extended finite element method (XFEM). In this coupled model, some important aspects in the

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